The present invention relates to a method for controlling an internal combustion engine.
In the control of fuel injection systems, the conventional practice utilizes electronic control units having volatile and non-volatile memory, input and output driver circuitry, and a processor capable of executing a stored instruction set, to control the various functions of the engine and its associated systems. A particular electronic control unit communicates with numerous sensors, actuators, and other electronic control units necessary to control various functions, which may include various aspects of fuel delivery, transmission control, or many others.
Fuel injectors utilizing electronic control valves for controlling fuel injection have become widespread. This is due to the precise control over the injection event provided by electronic control valves. In operation, the electronic control unit determines an energizing or excitation time for the control valve corresponding to current engine conditions. The excitation of the control valve causes a cascade of hydraulic events leading to the lifting of the spray tip needle, which causes fuel injection to occur.
With increasing demands for fuel economy, emission control, and other aspects of engine performance, there is a need for a method of controlling an internal combustion engine with greater precision than existing control techniques.
It is therefore an object of the present invention to provide a method of controlling an internal combustion engine in real time based on cylinder pressure measurements taken during the engine cycle.
In carrying out the above object and other objects and features of the present invention, a method of controlling an internal combustion engine including an engine block defining a cylinder and a piston received in the cylinder is provided. The method comprises determining a position of the piston within the cycle, and determining a pressure within the cylinder, when the piston is at the determined position, with a pressure sensor disposed in the cylinder. The method further comprises controlling the engine in real time based on a series of cylinder pressures and corresponding piston positions.
Embodiments of the present invention are suitable for a diesel engine. Further, in a preferred implementation, the engine operates over a four stroke cycle including an intake stroke, a compression stroke, a power stroke, and an exhaust stroke.
In one embodiment, the method further comprises determining the position of the piston within the cycle at first, second, and third points on the compression stroke. Pressure within the cylinder is determined with the pressure sensor for the first, second, and third points on the compression stroke. The method further comprises determining a linear status of the compression stroke based on the cylinder pressures and corresponding piston positions for the first, second, and third points on the compression stroke. Advantageously, a linear increase in the logarithm of pressure with respect to the logarithm of volume during the compression stroke means that leakage is minimal.
In one embodiment, the method further comprises determining the position of the piston within the cycle at a plurality of points on the compression stroke and a plurality of points on the power stroke. The pressure within the cylinder is determined with a pressure sensor for the plurality of points on the compression stroke and the plurality of points on the power stroke. The method further comprises determining a net work for the cycle based on the cylinder pressures and the corresponding piston positions for the plurality of points on the compression stroke and the plurality of points on the power stroke. Advantageously, in a multiple cylinder engine, the engine may be controlled in real time to balance the power output among the multiple cylinders by, over time, measuring the net work during a cycle from each cylinder and compensating for varying work per cylinder by, for example, adjusting the fuel pulse width for each cylinder.
In some embodiments, the method further comprises determining a peak cylinder pressure for the cylinder. Further, in some embodiments, the engine includes an intake pressure sensor, and the method further comprises determining the position of the piston within the cycle at a point on the intake stroke. The method further comprises determining the pressure within the cylinder with the pressure sensor for the point on the intake stroke, and determining the intake pressure from the intake pressure sensor. An offset or zero drift of the cylinder pressure sensor is calibrated based on the intake pressure from the intake pressure sensor.
In preferred embodiments of the present invention, the pressure sensor in the cylinder has a logarithmic output. A logarithmic output sensor is preferred because during the engine cycle, the logarithm of pressure varies linearly with respect to the logarithm of volume. In the alternative, a linear output sensor may be used, but using a linear output sensor would require a larger output range for the sensor and greater precision. For example, when a sensor has an analog output, a logarithmic output sensor could require merely a 10-bit converter, while a linear output sensor would require at least a 16-bit analog-to-digital converter to input the sensor signal to the engine controller.
Further, in carrying out the present invention, a method of controlling an internal combustion engine including an engine block defining a plurality of cylinders and a plurality of pistons, with each piston received in a corresponding cylinder, is provided. The method comprises determining a position of each piston within the cycle, and measuring a pressure within each cylinder, when the corresponding piston is at the determined position. The method further comprises controlling the engine in real time based on a series of cylinder pressures, and the corresponding piston positions for the plurality of cylinders and corresponding plurality of pistons.
Still further, in carrying out the present invention, an internal combustion engine is provided. The internal combustion engine comprises an engine block defining a plurality of cylinders, a plurality of pistons with a piston received in each cylinder, and a plurality of pressure sensors with a pressure sensor configured at each cylinder to detect cylinder pressure. A crankshaft has an encoder and drives the pistons. A crankshaft sensor detects a position of the crankshaft, and allows determination of the position of each piston within its cycle. The engine further comprises a controller configured to determine a pressure within each cylinder and the position of each corresponding piston within its cycle. The controller is further configured to control the engine in real time based on a series of cylinder pressures and corresponding piston positions.
The advantages associated with embodiments of the present invention are numerous. For example, embodiments of the present invention allow real time based feedback control over the combustion process and the four stroke cycle of the engine based on a series of cylinder pressures and corresponding piston positions as detected by various engine sensors. It is appreciated that xe2x80x9cin real timexe2x80x9d as used herein means that a plurality of measurements taken in one or more cycles of the piston would be used to control successive cycles, sometimes called control feedback, and/or to alert the operator of an undesirable condition and/or record an event for later diagnosis. The term xe2x80x9cin real timexe2x80x9d as viewed in the context of the present invention is distinguished from the capture of data for academic or research purposes to be utilized at a later time or in another engine. Further, the present invention is far different than the detection of solely the maximum cylinder pressure. For example, a pressure sensor may be located in each cylinder, and a crankshaft sensor may trigger the measurements of those pressures to correspond with the crankshaft positions. Advantageously, the real time control may be utilized to achieve accurate and precise emission control and fuel economy. Further, embodiments of the present invention may utilize real time control to compensate for cylinder variabilities including injector variabilities, cylinder or injector wear and change over time, and for various operating conditions such as, for example, when a turbocharger compressor wheel becomes dirty. The real time control provided by embodiments of the present invention allows sophisticated and advanced controls with such precision to allow control of emissions during transient engine conditions in some embodiments. Embodiments of the present invention may be implemented by utilizing a crankshaft encoder and sensor along with a pressure sensor at each cylinder, such as a piezoresistive element. Embodiments of the present invention have many additional advantages than those specifically mentioned above, including the ability to diagnose failures in cylinders before damage occurs and to adapt the engine to changing operating conditions.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.